During the late 1960s a small group of weapons engineers developed the 13mm gyrojet round, a large rocket powered bullet.
The gunpowder burn rapidly builds up pressure inside the firearm, sending the bullet out of the barrel at hundreds if not thousands of feet per second.
Some hollow point rounds—such as Hornady Critical Defense ammunition—have a polymer dot in the center of the opening to aggressively drive bullet expansion.
Jacketed hollow points are considerably more lethal than regular bullet ammunition.
An evolution of the dum dum bullet, jacketed hollow points are copper-jacketed bullets with a hollow opening at the tip revealing the lead core.